An elevator installation comprises, in a conventional manner, an elevator cage, an elevator shaft in which the elevator cage moves and a drive unit for moving the elevator cage.
For reasons of safety, present-day elevator installations are designed so that a protective space in the form of a shaft pit is located at the shaft base in order to ensure that maintenance personnel in the shaft are not placed at risk when the elevator cage travels into the lowermost position in the shaft. Typically, an elevator installation is also designed so that a protective space is located at the upper end of the shaft—called shaft head—so that maintenance personnel undertaking maintenance on the roof of the cage are not put at risk when the cage travels into the uppermost position of the shaft.
This occurs with the most diverse forms of elevator layouts, such as, for example, cable elevators, hydraulic elevators, linear motor elevators, etc.
Due to the safety regulation that a protective space has to be provided in the form of a shaft pit at the lower shaft end, the constructional height of the elevator shaft is higher than actually necessary from the purely technical aspect.
The protective space at the lower shaft end currently has typically a height of 50 cm plus the length of the buffer compressed to a maximum, the buffer being disposed at the shaft base in order to cushion the counterweight or the elevator cage.
An elevator installation with protective space at the lower and upper shaft end is longer by a few meters than the actual floor height of the building served by the elevator. This frequently leads to solutions in which the elevator shaft projects beyond the building. In earlier elevator layouts a part of the drive unit was usually mounted in an engine room above the shaft, i.e. either the elevator installation was dimensioned so that the uppermost floor was not served, since here the engine room inclusive of protective space was located, or the engine room inclusive of protective space was realized on the roof of the building.
With present-day elevator layouts the starting point has fundamentally changed, since increasingly elevator installations are realized in which the drive unit is arranged within the shaft space (elevator without engine room). Nevertheless, even here a protective space has to be planned in at the lower and/or upper shaft end due to regulations, which can be disadvantageous for the aesthetics of the building.
Apart from the aesthetic and constructional problems which result from the necessity of the protective spaces, these protective spaces cause additional costs in the erection of a building.
In current elevator layouts the entire installation is shut down in the case of maintenance. This frequently leads to problems if no other elevator is provided in the same building or if the conveying capacity of the other elevators is insufficient.
It is also important with current elevator layouts that maintenance, assembly, repair or inspection personnel at the base of the elevator shaft or at the head end of the same have access to the various technical and electrical systems.
European Patent Application EP 1052212-A describes equipment which allows work to be carried out in an elevator shaft. According to this patent application a protective space is realized at the upper shaft end in that the counterweight is prematurely stopped at the lower shaft end. The cage—which is connected with the counterweight by way of a cable system—thereby cannot be moved up to the shaft head.
U.S. Pat. No. 6,223,861 describes a safety system for an elevator in which the elevator is moved only at reduced speed if a person stands in the elevator shaft. Whether a person stands in the elevator shaft is ascertained by sensors at the shaft doors. If the elevator moves at reduced speed, special switches at the lower and upper shaft ends stop the cage in order to prevent movement of the cage into the protective space.
Another form of safety system is disclosed in U.S. Pat. No. 6,138,798. In order to ensure the safety of maintenance personnel in the shaft pit, buffers are used, the length of which can be changed. If a person is detected in the region of the shaft pit, the buffers are driven out in order to thus be able to guarantee a protective space of greater height.
A similar approach is known from Japanese Patent Abstract with publication number 0905894, wherein, however, this specification concerns the protection zone at the shaft head.
An electronic safety bus connecting different sensors with a central controller is described in U.S. Pat. No. 6,173,814. An elevator installation based on a safety bus of that kind is particularly safe, since the elevator can be stopped directly when an exceptional situation is detected.